1. Field of the Invention
The invention relates to a method and apparatus for the production of liquid iron from iron oxide, wherein the iron ore oxide is reduced at least partly to sponge iron by a reducing gas in a reduction column, whereafter the sponge iron is melted in a melt vessel and then tapped, oxygen-containing gas and carbon-containing material being caused to react together in the melt vessel to generate the required melting heat and the said reducing gas.
2. Description of the Prior Art
The most commonly used method of producing liquid iron from iron ore is the blast furnace process. The resultant so-called pig iron contains approximately 4 to 5.5% carbon, together with amounts of silicon, sulphur, phosphorus and other desirable or undesirable elements, dependent on the operation of the blast furnace. These additives must be at least partly removed by means of a subsequent process in a steel furnace, if steel is to be produced from the pig iron.
The blast furnace process has several disadvantages. Firstly it is based on the use of coke, for which separate coking plants are required, and as a result of which the reduction process in the blast furnace requires the indirect use of high-quality, expensive coking coal. Secondly, the entire wall structure must be constructed for a high thermal load, which gives rise to complicated and expensive structures. Thirdly expensive blast preheating devices are employed. The high content of undesirable elements in the pig iron derived from a blast furnace should also be regarded as a disadvantage.
To overcome these disadvantages, processes have been proposed in which iron ore is converted to sponge iron at a lower temperature by means of reducing gases. This sponge iron is then melted further in an electric furnace, and converted to steel. In this process the reduced sponge iron is usually cooled, before feeding to the electric furnace. The associated heat losses affect the cost price of the final steel most unfavourably.
This process also suffers from the disadvantage that separate production of the necessary reducing gas is required. Moreover, the costs of electricity associated with the operation of an electric furnace often prevent economic application. DE-A-No. 2550761 describes an attempt made to overcome these difficulties. In this case, material containing carbon is fed into a melt vessel below the liquid level of an iron bath, causing the iron to be saturated and maintained with dissolved carbon. Sponge iron and/or iron oxide, together with oxygen, is blown on to the bath by means of a liquid-cooled lance. As a result of the reactions thereby initiated, carbon from the bath is converted with oxygen to CO gas, whilst the sponge iron is melted by the heat thereby released. If non-reduced oxide is also supplied, this is reduced by the carbon present in the bath. The CO gas formed is discharged and used elsewhere as a reducing gas for the formation of sponge iron from iron ore. After the level of the molten iron has risen above a certain point, iron can be tapped off. In this case, however, sufficient iron must remain to act as the reagent. The iron drained off is rich in carbon.
Others have more recently proposed processes in which the sponge iron is fed directly into a melt vessel which is located below the reduction column, and the reducing gas and the melting heat are produced by the reaction, in the melt vessel, of oxygen-containing gas and carbonaceous material which are fed into the melt vessel above the surface of the liquid iron bath therein. Examples of such proposals are U.S. Pat. Nos. 4,111,687, 4,248,626 and 4,316,739.
According to U.S. Pat. No. 4,111,687, the preferred fuels in the melt vessel are oxygen and natural gas. In this case, the melt vessel is in open communication with the reduction column. In U.S. Pat. No. 4,248,626 the use of powdered coal and oxygen is described, these being fed through injection pipes to above the liquid iron in the melt vessel, while in U.S. Pat. No. 4,316,739 powdered coal and oxygen are directed onto a pile of hot reduced iron pellets on a platform in the melt vessel. In both these last two proposals, the reducing gas produced in the melt vessel is taken off for separate treatment, before being fed into the reduction column.